Several processes for producing low-lactose and lactose-free milk by using membrane techniques are known. A conventional enzymatic process for splitting lactose is also generally known in the field, the process comprising the step of adding lactase from fungus or yeast into milk in such a manner that lactose is split into monosaccharides, i.e. glucose and galactose, in over 80%.
Several membrane filtration process solutions have been presented for removing lactose from milk raw material. Four basic membrane filtration processes are generally used: reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). Of these, UF is mainly suitable for separating lactose from milk. Reverse osmosis is generally applied to concentration, ultra- and microfiltration to fractionation, and nanofiltration to both concentration and fractionation. A lactose removal process based on a membrane technique is described in WO publication 00/45643, for instance, wherein lactose is removed by ultrafiltration and diafiltration.
It is known in the field that a problem with membrane techniques in general is that during ultrafiltration not only lactose is removed from the milk, but also some of the minerals that are significant for the taste of milk and milk products prepared thereof. Controlling the mineral content and especially bivalent minerals, such as calcium and magnesium, is particularly problematic in the field, and extensive loss results from the known processes, which is why these bivalent minerals must often be returned or added separately.
Often membrane processes also produce, for instance, mineral-containing secondary flows, which cannot be exploited efficiently and which also increase waste water load, require further processing and add to the costs. It would thus be useful to provide processes, by which bivalent minerals in particular may be controlled in the process and recovered more efficiently, thus allowing the circulation of process waters without producing secondary flows.
WO publication 03/094623 A1 discloses a process in which a milk product is ultrafiltered, nanofiltered, and concentrated by reverse osmosis, after which the minerals removed during ultrafiltration are returned to the UF retentate. The residual lactose of the thus obtained low-lactose milk product is hydrolyzed with a lactase enzyme into monosaccharides, whereby an essentially lactose-free milk product is obtained. With this process, lactose is removed from milk without affecting the organoleptic properties of the milk product being prepared. In this process, the loss of bivalent minerals, such as calcium and magnesium, may be significant. Also, the process produces minerals containing secondary flows, which cannot be utilized in the process and which require post-processing. To solve these problems, simpler and more efficient alternative processes are needed.
Lactose can also be specifically separated from milk by chromatography. However, many problems differing from the processing of whey are associated with the processing of milk, such as easy precipitation of casein, maintaining the micellar structure of casein, behaviour of fat, and extremely strict hygiene requirements. For instance EP publication 226035 B1 describes a lactose separation process in which milk is fractionated in such a manner that the lactose fraction is separated and the minerals are in the protein fraction or protein-fat fraction. The process is characterized by balancing cation exchange resin by making its cation composition correspond to that of milk, and milk is separated chromatographically in a column with the balanced cation exchange resin at a temperature of approximately 50 to 80° C. by using water in elution. An advantage of the process is that all compounds essential to taste remain in the milk. However, chromatographic lactose separation is a slow and complex process that cannot be directly applied to conventional dairies without expensive equipment investments. Another problem is a high consumption of water and a large amount of chemicals.
Patent publication KR20040103818 describes a process for the production of low-lactose milk, comprising nanofiltering milk hydrolyzed with lactase to partly remove galactose and glucose, and adding water into the nanofiltration retentate to achieve a suitable sweetness. Choi et al. (Asian-Aust. J. Anim. Sci 20 (6) (2007) 989-993) describe a process for the production of lactose-hydrolyzed milk, wherein raw milk is hydrolyzed with β-galactosidase (5 000 lactase activity unit/g, Validase, Valley Research) partly (0.03%, 4° C., 24 hours) or ‘completely’ (0.1%; 40 h), heat-treated to inactivate the enzyme (72° C., 5 min), cooled to 45 to 50° C., and nanofiltered at a pressure of approximately 9 to 10 bars (130 to 140 psi; concentration factor 1.6) Water was added into the NF retentate and the heat treatment was performed at 65° C. for 30 min. The lactose-hydrolyze milk consisted of protein (3.1%), fat (3.5%), lactose (0.06%) glucose (1.45%), and galactose (1.29%). In the processes described in said publications and comprising a single-phase nanofiltration, all of the monovalent minerals are not yet returned to milk efficiently enough.
WO publication 2007/076873 describes low-carbohydrate milk containing essentially all of the calcium and protein of the original milk, and a process for the production thereof. In this process, the pH of milk is adjusted to an alkaline value of 7.0 to 9.5, the milk is ultrafiltered, the UF permeate is nanofiltered preferably at a temperature of approximately 10° C. to minimize the microbiological risk, the NF permeate, UF retentate and water are combined, and the pH is adjusted to the pH value of the original milk (pH 6.7) by adding acid, preferably citric acid or phosphoric acid. The energy content of the product is 90 to 250 kJ/100 g. The process comprises a plurality of steps and requires strong chemicals to adjust the pH and to minimize the calcium and protein loss.
WO publication 2004/019693 describes a process for separating different components with membrane techniques (ultrafiltration, nanofiltration and reverse osmosis) and combining these components into milk products, such as ice cream, yogurt and milk drink.
It is also known to use milk after lactose removal as a raw material in the production of low-carbohydrate dairy products. For instance WO publication 2006/087409 A1 describes a low-energy skim milk drink rich in added calcium, containing a low-energy milk base, which consists of skim milk or a whey protein solution or a mixture thereof and from which carbohydrates have been removed either completely or partly by ultrafiltration or chromatography according to the previously known processes. The energy content of the product is 20 kcal/100 g at most.
Recent studies have concentrated on membrane filtration of milk and on the use of such filtered, low-carbohydrate milk in the preparation of dairy products, such as cheese, ice cream and yogurt. Common to the known multi-step membrane filtration processes comprising several different processes, one sub-phase of which is nanofiltration, for preparing low-carbohydrate milk products is that residual lactose is not removed from the milk raw material until it has undergone membrane filtration.
It is very challenging to achieve products that are completely flawless in taste and structure, that meet the consumers' expectations on an organoleptically competent milk product, and that are produced economically and simply without losing polyvalent minerals.
A process for the production of low-lactose and lactose-free milk products that are completely flawless in their organoleptic properties without any extra costs has now been unexpectedly invented. The process of the invention makes it possible to control bivalent minerals more efficiently and simpler than in conventional processes without any extra costs, and allows to minimize losses. In addition, the process of the invention does not produce secondary flows requiring post-processing, which makes the process more efficient.